To adhere to a standard of “one person, one vote,” the Supreme Court requires each congressional district to contain a roughly equal number of people. The court has also ruled that gerrymandering legislative maps to dilute the power of racial minorities is unlawful (though its commitment to that view might be questioned).

However, the court has avoided taking a stand on partisan gerrymanders, by which legislative maps are manipulated to give a decisive advantage to one party over another. This month, it sent claims on gerrymandered districts in several states back to lower courts.

That’s unfortunate. Political gerrymanders, whether by Democrats or Republicans, undermine confidence in the political system, add to an already abundant supply of partisan rancor, and discriminate against the Americans whose votes are discounted.

Map drawing is still largely in the hands of state politicians. That poses not one but two conflicts of interest. Incumbent legislators want to ease their reelection. (Hence the complaint that gerrymandering lets elected officials “choose their voters.”) And each political party wants to stack the deck in its favor.

State legislatures draw state legislative districts in 32 states and draw congressional districts in 34. A handful of states use some form of commission to advise politicians. Only two — Arizona and California — have districts drawn by an independent commission separated by design from legislative control. But commissions, albeit with varying degrees of independence, appear to be gaining momentum. The court upheld their constitutionality in 2015, and Arkansas, Michigan, Missouri, Oklahoma and Utah all have initiatives to establish redistricting commissions.

Commissions are a giant step in the right direction, but they’re not foolproof. Some aren’t truly independent. And even the most independent commissions must be wary of being compromised. In California, Democratic politicians vigorously opposed the state’s 2010 ballot initiative empowering a citizen commission to draw congressional boundaries. After the initiative passed, and the commission began soliciting public input, some Democratic partisans tried to influence it surreptitiously.

Still, independent commissions are the best bet for drawing maps that are fair, compact, respectful of municipal and county lines and mindful of maintaining “communities of interest” so that like-minded neighborhoods don’t have their votes fractured across multiple districts. Early warnings that citizens lacking political experience would be flummoxed by such a delicate exercise have proved groundless. In both Arizona and California, the amateurs are doing just fine.

The Brennan Center for Justice at New York University has produced a list of best practices, stressing above all an “independent selection process” that screens potential commission members for conflicts of interest and other disqualifying factors. Partisan gerrymanders are not the source of partisan polarization — but they surely don’t mitigate it. As more states look for alternatives, nonpartisan, independent commissions are the way to go.